Optical switch and MEMS package

Abstract

An optical switch switches ports through which a beam is input and output and includes an optical system through which the beam passes; a movable reflector that is enclosed in a casing and reflects, at a variable angle, the beam that has passed through the optical system; and a transmissive window that is disposed in the casing at a position through which the beam passes, is made of a uniaxial crystal, and obtains a phase difference with respect to the beam passing therethrough having a wavelength λ. The phase difference is λ/4 times a positive odd integer and results from a setting of an orientation of a crystal axis and a thickness of the transmissive window.

1. An optical switch comprising:
 a plurality of ports through which a beam is input and output; 
 an optical system through which the beam passes; 
 a movable reflector that is enclosed in a casing and reflects, at a variable angle, the beam that has passed through the optical system; and 
 a transmissive window that is disposed in the casing at a position through which the beam passes, is made of a uniaxial crystal, and obtains a phase difference with respect to the beam passing therethrough having a wavelength λ, the phase difference being ·λ/4 times a positive odd integer and resulting from a setting of an orientation of a crystal axis and a thickness of the transmissive window, wherein 
 the thickness of the transmissive window is distributed in a direction in which the ports are arranged such that the phase difference is obtained irrespective of the port through which the beam passes. 
 
   
   
     2. The optical switch according to  claim 1 , wherein
     t ( x )=(2 m +1)×λ/(4 ×F ( x )) 
 
     is satisfied, where
 x is a position x of the ports respectively; 
 t(x) is the thickness of the transmissive window at a position through which the beam transmitted from the port at the position x passes; 
 F(x) is a function determined from the orientation of the crystal axis, birefringence of the transmissive window, and an angle of the beam passing therethrough; and 
 λ is the wavelength λ. 
 
   
   
     3. The optical switch according to  claim 2 , wherein t(x) is approximated by a linear function. 
   
   
     4. The optical switch according to  claim 1 , wherein the transmissive window is tilted at a given angle with respect to a direction in which the ports are arranged. 
   
   
     5. The optical switch according to  claim 1 , wherein
 the optical system includes
 a dispersing element that separates the beam passing therethrough into components according to wavelength, and 
 a converging lens that respectively converges the components, and 
 
 the movable reflector is disposed in plurality in an array corresponding to each of the components respectively converged by the converging unit. 
 
   
   
     6. The optical switch according to  claim 5 , wherein the dispersing element includes a plurality of diffraction gratings through which the beam passes. 
   
   
     7. The optical switch according to  claim 1 , wherein the uniaxial crystal is a sapphire crystal. 
   
   
     8. A MEMS package comprising:
 a movable reflector that reflects a beam at a variable angle; 
 a casing that encloses the movable reflector; and a transmissive window that is disposed in the casing at a position through which the beam passes, is made of a uniaxial crystal, and obtains a phase difference with respect to the beam passing therethrough having a wavelength λ, the phase difference being ·λ/4 times a positive odd integer and resulting from a setting of an orientation of a crystal axis and a thickness of the transmissive window, wherein 
 the thickness of the transmissive window is distributed in a direction in which the ports are arranged such that the phase difference is obtained irrespective of the port through which the beam passes. 
 
   
   
     9. An optical switch comprising:
 a plurality of ports through which a beam is input and output; 
 an optical system through which the beam passes; 
 a movable reflector that is enclosed in a casing and reflects, at a variable angle, the beam that has passed through the optical system; and 
 a transmissive window that is disposed in the casing at a position through which the beam passes, is made of a uniaxial crystal, and obtains a phase difference with respect to the beam passing therethrough having a wavelength λ, the phase difference being ·λ/4 times a positive odd integer and resulting from a setting of an orientation of a crystal axis and a thickness of the transmissive window, wherein 
 a surface of the transmissive window is tilted at a given angle with respect to a direction in which the ports are arranged.